1. Field of the Invention
The present invention relates to a combinational weighing or counting method and an apparatus therefor which utilizes a plurality of weighing devices for weighing or counting a plurality of articles of varying weight such as, for example, snacks, candies, fruits or vegetables or small machine parts, and then to select an appropriate combination of the articles based on results of weight measurements or counts.
2. Description of the Prior Art
The combinational weighing apparatus is a machine so designed that the articles of varying weight such as snacks, candies, fruits or vegetables can be averaged or substantially matched in weight to a target combined weight. An example of this combinational weighing apparatus is well known and is disclosed in, for example, the Japanese Laid-open Patent Publication No. 63-30725 published in 1988, and will now be discussed with reference to FIG. 6.
Referring to FIG. 6, articles M to be weighed which have been transported by means of a transport conveyor 1 are dispensed through a dispensing feeder 2 into a plurality of vibratory feeders or driving feeders 3.sub.1 to 3.sub.n which subsequently loads fractions of the articles into respective weighing hoppers 6.sub.1 to 6.sub.n. A combination control means (not shown) selects some of the weighing hoppers 6.sub.1 to 6.sub.n to thereby select an appropriate combination of the weighing hoppers 6.sub.1 to 6.sub.n. In other words, based on the weights given by the respective weighing hoppers 6.sub.1 to 6.sub.n, the combination control means selects the appropriate combination of the weighing hoppers 6.sub.1 to 6.sub.n which would eventually provides a measured combined weight equal or generally equal to a target combined weight. The respective fractions of the articles M accommodated within the selected appropriate combination of the weighing hoppers 6.sub.1 to 6.sub.n are then discharged into a collecting and discharging chute 9.
According to the prior art, in order to accomplish the selection of the appropriate combination as precisely and as efficiently as possible, arrangement has hitherto been made that the amount of the articles M to be supplied into each of the weighing hoppers 6.sub.1 to 6.sub.n is equal or approximately equal to a target supply weight T (for example, the quotient of the target combined weight T.sub.M divided by the number m of the weighing hoppers selected for the combination) to which the articles are supplied into the respective weighing hoppers 6.sub.1 to 6.sub.n. For this purpose, parameters for controlling a supply ability of each of the driving feeders 3.sub.1 to 3.sub.n (such as representative of the amplitude of vibration to which each driving feeder is vibrated and the vibrating time over which such driving feeder is vibrated) are controlled in the following manner.
A parameter setting means (not shown) determines, for each of the driving feeders 3.sub.1 to 3.sub.n, parameters for the current weighing cycle on the basis of the parameters for the previous weighing cycle and the amounts of the articles actually supplied into the weighing hoppers 6.sub.1 to 6.sub.n during the previous weighing cycle. The driving feeders 3.sub.1 to 3.sub.n are vibrated according to the parameter so determined for the current weighing cycle that the amounts of the articles M corresponding to the target supply weight T can be supplied into the respective weighing hoppers 6.sub.1 to 6.sub.n.
The target supply weight T referred to above is determined in the following manner. Assuming that the number of the weighing hoppers 6.sub.1 to 6.sub.n is 10 (i.e., n=10), arbitrarily chosen number m of the ten weighing hoppers will give the maximum number of calculated weights (combinational calculated weights) when the number m of the weighing hoppers is 5. Accordingly, the value of the target combined weight T.sub.M divided by the arbitrarily chosen number, that is, 5, of the weighing hoppers is chosen as the target supply weight T. In this way, the combinational calculated weight W.sub.M given by summing one or a number n of measured weights W.sub.1 together gives rise to a distribution shown by the phantom line in FIG. 1(b), showing the highest probability at a weight corresponding to the target combined weight T.sub.M.
On the other hand, the weight of articles packed in, for example, a bag, that is, the combination selected weight W.sub.S, is selected out from the combinational calculated weight W.sub.M in the following manner. The combinational calculated weight W.sub.M has an allowance ranging between a predetermined lower limit T.sub.MIN and a predetermined upper limit T.sub.MAX and, accordingly, the value within the allowance between the lower limit T.sub.MIN and the upper limit T.sub.MAX of the combinational calculated weight W.sub.M is selected for the combination selected weight W.sub.S. In other words, an area S2 hatched by the phantom lines in FIG. 1(b) is selected for the combination selected weight W.sub.S.
As discussed hereinabove, since the combinational calculated weight W.sub.M is so determined as to occur at the target combined weight T.sub.M with the highest probability, the probability with which the combinational calculated weight W.sub.M takes a value slightly smaller than the target combined weight T.sub.M is comparable to the probability with which the combinational calculated weight W.sub.M is slightly greater than the target combined weight T.sub.M. However, since the target combined weight T.sub.M is generally equal to the lower limit T.sub.MIN, the combinational calculated weight W.sub.M which is of a value slightly smaller than the target combined weight T.sub.M which occurs with a high probability is not selected for the combination. Accordingly, the prior art method has a problem in that, even though weight measurement is carried out, cases often occur in which no combinational selection is carried out.
Where no combinational selection occurs even though the weight measurement has been carried out, it requires, for example, that all of the articles M within the respective weighing hoppers 6.sub.1 to 6.sub.n must be discharged to the outside through the collecting and discharging chute 9 and, therefore, it brings about an additional problem in that the time required to complete each cycle of packing of the articles tends to be prolonged. It is to be noted that similar problems occur with the combinational counting apparatus.